Methods of forming spherical metallic particles

ABSTRACT

A method of forming titanium-based spherical metallic particles includes contacting a feedstock material including a metal halide with a reductant in the presence of a microwave plasma discharge.

BACKGROUND

Embodiments of the present disclosure generally relate to methods of forming spherical titanium-based metallic particles. More particularly, embodiments of the present disclosure relate to methods of forming spherical titanium alloy particles using microwave plasma.

An important aspect of preparing some forms of industrial powders is the spheroidization process, which transforms irregularly shaped or angular powders produced by conventional crushing methods, into spherical low-porosity particles. Spherical powders are homogenous in shape, dense, less porous, and exhibit better flowability. Such powders may exhibit superior properties in applications such as injection molding, thermal spray coatings, or additive manufacturing.

Titanium and titanium-alloy particles are particularly useful in additive manufacturing of industrial grade components. Additive manufacturing of titanium components may require high-quality, low-cost spherical titanium or titanium alloy powder as a feedstock for good flowability. Conventional methods for processing of titanium alloys to produce spherical powders typically involve multiple steps, such as, producing titanium ingots from sponges and utilizing melting and atomization processes on the titanium ingots to produce spherical powder. The formation of titanium powder can be facilitated by one of several approaches, such as, the Kroll process, the Hunter process, or the Armstrong process. However, most of these commercial processes are typically carried out as large-scale processes and are batch segregated, which increases the complexity and associated cost. Furthermore, the intermediate metallurgical processes for conversion to alloys may add to the cost of the resulting spherical titanium alloy powder.

Other methods for forming spherical titanium particles employ thermal arc plasma or radio-frequency generated plasma for spheroidization of titanium-based feedstock material. However, these two methods may present limitations inherent to the thermal non-uniformity of radio-frequency and thermal arc plasmas. Some other spheroidization methods employ inductively coupled plasma (ICP), where angular powder obtained from a Hydride-Dehydride (HDH) process is entrained within a gas and injected though a hot plasma environment to melt the powder particles. However, this method also suffers from non-uniformity of the plasma, which leads to incomplete spheroidization of the feedstock. Further, the HDH process involves several time-consuming complex steps, which may again add to the cost of the resulting spherical powder.

BRIEF DESCRIPTION

In one aspect, the present disclosure relates to a method of forming spherical metallic particles including titanium. The method includes contacting a feedstock material including a metal halide with a reductant in the presence of a microwave plasma discharge to form the spherical metallic particles. In another aspect, the present disclosure relates to a plurality of spherical metallic particles including titanium, formed by contacting a feedstock material including a titanium halide with a reductant in the presence of a microwave plasma discharge.

In yet another aspect, the present disclosure relates to a method of forming spherical titanium-based particles. The method includes contacting a feedstock material including a titanium halide with a hydrogen gas in the presence of a microwave plasma discharge to reduce the titanium halide and form the spherical titanium-based particles.

DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein:

FIG. 1 illustrates a schematic of an apparatus for forming spherical metallic particles, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings. The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. As used herein, the term “or” is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value solidified by a term or terms, such as “about”, and “substantially” is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Similarly, “free” may be used in combination with a term, and may include an insubstantial number, or trace amounts, while still being considered free of the solidified term. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

As mentioned earlier, conventional methods for producing spherical titanium-based particles may involve expensive feedstock material such as metallic sponges. Further, these processes may involve multiple intermediate metallurgical steps and batch processing of the feedstock material, which in turn may affect the cost and consistency of the final product. Embodiments of the present disclosure described herein address the noted shortcomings in the art.

A method of forming spherical metallic particles including titanium is presented. The method includes contacting a feedstock material including a metal halide with a reductant in the presence of a microwave plasma discharge.

The term “metallic particles” as used herein refers to a plurality of particles including an elemental metal, a metal alloy, or a combination thereof. Therefore, the term metallic particles as used herein includes elemental titanium, a titanium-based metal alloy, or a combination thereof. The term “elemental metal” as used herein means that an amount of a base metal in the metallic particles is greater than 97 weight percent. In certain embodiments, an amount of the base metal in the metallic particles is greater than 99 weight percent. Therefore, the term “elemental titanium” as used herein means than an amount of titanium in the metallic particles is greater than 97 weight percent. In certain embodiments, the spherical metallic particles include a metal alloy including titanium. The metal alloy may further include aluminum, vanadium, or a combination thereof. In certain embodiments, the spherical metallic particles include titanium alloy particles, such as, Ti6Al4V. In some such instances, the amount of aluminum in the titanium alloy may be in a range of from about 4 weight percent to about 7 weight percent, and the amount of vanadium in the titanium alloy may be in a range from about 3 weight percent to about 5 weight percent.

The term “spherical metallic particles” as used herein refers to a plurality of particles having an average aspect ratio that is less than 1.1. In some embodiments, the spherical metallic particles may have an average aspect ratio that is less than 1.05. The spherical metallic particles may have an average diameter in a range of from about 1 micron to about 500 microns. In some embodiments, the spherical metallic particles may have an average diameter in a range of from about 10 microns to about 150 microns.

As noted herein, the method includes contacting the feedstock material with the microwave plasma discharge. The feedstock material includes a metal halide such as titanium halide. In embodiments, wherein the spherical metallic particles include elemental titanium, the feedstock material includes at least one titanium halide. A non-limiting example of a suitable titanium halide includes titanium chloride.

In some embodiments, wherein the spherical metallic particles include a metal alloy, the feedstock material includes a metal halide mixture. Non-limiting examples of suitable halides in the metal halide mixture may include titanium chloride and one or both of vanadium chloride and aluminum chloride. In certain embodiments, the feedstock material may be in the form of a liquid.

The microwave plasma discharge may be generated using a suitable microwave plasma torch. The method may include introducing the feedstock material into the microwave-plasma torch using any suitable means, for example, a fluidized bed feeder. Within the microwave plasma torch, the feedstock materials are exposed to a plasma discharge causing the materials to melt. Because of the uniformity of the microwave plasma discharge, the feedstock material may be exposed to a substantially uniform temperature profile, and rapidly heated and melted. In one example, the feedstock material may be exposed to a uniform temperature profile in a range from about 4,000 K to about 8,000 K within the plasma. During the same time (i.e., time that the feedstock material is exposed to the plasma discharge), a reductant may be introduced into the microwave plasma torch such that the reductant also contacts the feedstock material. Therefore, the metal halide in the feedstock material undergoes a reduction reaction, thereby forming a metal or a metal alloy (depending on the feedstock material composition). A non-limiting example of a suitable reductant includes hydrogen. In certain embodiments, the reductant includes hydrogen gas.

After the reduction of the metal halides in the feedstock material, within the microwave plasma discharge, the reduced and melted metals may be inherently spheroidized, at least in part, due to liquid surface tension. As the microwave generated plasma exhibits a substantially uniform temperature profile, more than 90% spheroidization of particles may be achieved. Therefore, by exposing the feedstock material to the microwave plasma discharge in the presence of the reductant, both dehalogenation and spheroidization are achieved. Thus, separate or distinct processing steps may not be needed to achieve dehalogenation and spheroidization.

Various parameters of the microwave plasma discharge, as well as feedstock material parameters, may be adjusted in order to achieve the desired results. These parameters may include one or more of microwave power, feedstock material size, feedstock material insertion rate, gas flow rates, plasma temperature, and cooling rates.

After the spheroidization step in the microwave plasma discharge, the plurality of spherical metallic particles may exit the microwave plasma discharge, resulting in cooling and further solidification of the particles. In some embodiments, the spherical metallic particles exiting from the microwave plasma discharge may be further subjected to one or more additional cooling steps to facilitate solidification and collection. The cooled and solidified spherical metallic particles may be subsequently collected using appropriate collection mechanisms, e.g., collection bins.

FIG. 1 illustrates a schematic of an apparatus 100 for forming spherical metallic particles, in accordance with some embodiments of the present disclosure. The apparatus includes a plasma torch 110 having a first inlet 101 and a second inlet 102. The plasma torch 110 is configured to generate and sustain a microwave plasma discharge 150 upon ignition from a suitable microwave radiation source 120. A feedstock material 130 is fed into the plasma torch 110 via the first inlet 101 and a reductant 140 is fed into the plasma torch 110 via the second inlet 102. As further illustrated in FIG. 1, the feedstock material 130 is introduced into the microwave plasma discharge 150 in the presence of the reductant 140. The feedstock material 130 melts within the microwave plasma discharge 150, and is simultaneously reduced within the microwave plasma discharge because of the reductant 140. The reduced and melted metals are inherently spheroidized, at least in part, due to liquid surface tension. Spherical metallic particles 160 are discharged from the plasma torch 110 via an outlet 103. The location and configuration of the first inlet 101, the second inlet 102, and the outlet 103 are depicted in FIG. 1 for illustration purposes only, and any other suitable locations and configurations are also envisaged within the scope of the present disclosure. As noted earlier, the discharged spherical metallic particles 160 may be subjected to one or more cooling steps and subsequently collected (not shown in FIGURE).

A method of forming spherical titanium-based particles is also presented. The method includes contacting a feedstock material including a titanium halide with a hydrogen gas in the presence of a microwave plasma discharge, to reduce the titanium halide and form the spherical titanium-based particles.

In one example, the method includes contacting liquid mixtures of titanium tetrachloride and other metal chlorides (such as aluminum and vanadium chlorides) to form a liquid halide mixture. The liquid halide mixture is used as a feedstock in a microwave-based plasma system containing a reducing atmosphere, for example, hydrogen gas. In the reducing atmosphere plasma environment, the metal halides are directly reduced to metal, and subsequently converted to spherical titanium alloy powder.

A plurality of spherical metallic particles including titanium, formed by the method described herein, is also presented. The plurality of spherical metallic particles includes an elemental metal, a metal alloy, or a combination thereof. In some embodiments, the spherical metallic particles include elemental titanium, a titanium alloy, or a combination thereof. In certain embodiments, the plurality of spherical metallic particles includes a titanium alloy. The titanium alloy may further include aluminum, vanadium, or a combination thereof.

The spherical titanium-based metallic particles and methods of producing such particles, in accordance with embodiments of the present disclosure, may provide a number of advantages. For example, the methods as described herein may allow for a continuous process that simultaneously reduces and spheroidizes the feedstock materials. That is, the separate and distinct steps required in conventional processes (e.g., HDH process) can be replaced with a single processing step using a microwave plasma discharge. Reduction in the number of intermediate steps may reduce the cost of the resulting spherical metallic particles. Further, use of simple metal halide mixtures as feedstock materials, instead of the more expensive traditional sponge-based feedstock materials may further significantly reduce the cost of the resulting spherical metallic particles.

Reduction in the number of processing steps also reduces the possibility for contamination by oxygen and other contaminants. Additionally, the continuous spheroidization process disclosed herein may improve the consistency of the end products by reducing or eliminating variations associated with typical batch-based dehydrogenation processes.

The methods as described herein can achieve additional improvements in consistency due to the homogeneity and control of the energy source (i.e., microwave plasma process). Specifically, if the plasma conditions are well controlled, particle agglomeration can be reduced, if not eliminated, thus leading to a better particle size distribution, which could result in high-quality, low-cost, high flowability titanium-based powder. As mentioned earlier, high-quality, low-cost, high flowability titanium-based powder may be particularly desirable for additive manufacturing of titanium-based components.

The appended claims are intended to claim the invention as broadly as it has been conceived and the examples herein presented are illustrative of selected embodiments from a manifold of all possible embodiments. Accordingly, it is the Applicants' intention that the appended claims are not to be limited by the choice of examples utilized to illustrate features of the present disclosure. As used in the claims, the word “comprises” and its grammatical variants logically also subtend and include phrases of varying and differing extent such as for example, but not limited thereto, “consisting essentially of” and “consisting of.” Where necessary, ranges have been supplied; those ranges are inclusive of all sub-ranges there between. It is to be expected that variations in these ranges will suggest themselves to a practitioner having ordinary skill in the art and where not already dedicated to the public, those variations should where possible be construed to be covered by the appended claims. It is also anticipated that advances in science and technology will make equivalents and substitutions possible that are not now contemplated by reason of the imprecision of language and these variations should also be construed where possible to be covered by the appended claims. 

1. A method of forming spherical metallic particles, comprising: contacting a feedstock material comprising a metal halide with a reductant in the presence of a microwave plasma discharge to form the spherical metallic particles, wherein the spherical metallic particles comprise titanium.
 2. The method of claim 1, wherein the spherical metallic particles comprise an elemental metal, a metal alloy, or a combination thereof.
 3. The method of claim 1, wherein the spherical metallic particles comprise a metal alloy comprising titanium.
 4. The method of claim 3, wherein the metal alloy further comprises aluminum, vanadium, or a combination thereof.
 5. The method of claim 1, wherein the metal halide comprises a titanium halide.
 6. The method of claim 5, wherein the metal halide comprises titanium chloride.
 7. The method of claim 1, wherein the feedstock material comprises a metal halide mixture.
 8. The method of claim 7, wherein the metal halide mixture comprises a titanium halide and one or both of a vanadium halide and an aluminum halide.
 9. The method of claim 1, wherein the feedstock material is a liquid.
 10. The method of claim 1, wherein the reductant comprises hydrogen.
 11. The method of claim 1, wherein the reductant comprises hydrogen gas.
 12. A plurality of spherical metallic particles comprising titanium, formed by contacting a feedstock material comprising a titanium halide with a reductant in the presence of a microwave plasma discharge.
 13. The plurality of spherical metallic particles of claim 12, wherein the plurality of spherical metallic particles comprises elemental titanium, a titanium alloy, or a combination thereof.
 14. The plurality of spherical metallic particles of claim 12, wherein the plurality of spherical metallic particles comprises a titanium alloy.
 15. The plurality of spherical metallic particles of claim 14, wherein the titanium alloy further comprises aluminum, vanadium, or a combination thereof.
 16. A method of forming spherical titanium-based particles, comprising: contacting a feedstock material comprising a titanium halide with a hydrogen gas in the presence of a microwave plasma discharge to reduce the titanium halide and form the spherical titanium-based particles.
 17. The method of claim 16, wherein the feedstock material further comprises a vanadium halide, an aluminum halide, or a combination thereof.
 18. The method of claim 16, wherein the spherical titanium-based particles comprise particles of a titanium alloy. 